About this. I think it would be great to have a Vanilla or BC or anything further server. I fear that even if they would be up, it would be very hard to please people once they really are up. Obviously, Vanilla had it's flaws. It didn't support some of the newer graphic technologies, netcode and it had weird bugs (like staying kneeled down when mining some nodes, and other weird stuff) which people playing those realms would have to take for granted.
These servers would most likely run the latest patch of that particular Xpack, not the transition patch or anything. People would complain they want to redo the opening of AQ, or something similar.
It will be very hard to get this right.
I personally wouldn't mind it beging a bit buggy, but it would have to come with a giant warning for non Vanilla players that the game was in a very different state from what it is now, and that some of that stuff just isn't going to get fixed because of it being part of the experience.